Many countries are running facilities for recovering V and Mo from spent petrochemical desulfurization catalyst, which contains a large amount of V and Mo.
Generally, V and Mo are recovered by mixing spent desulfurization catalyst with sodium carbonate, desulfurizing the mixture by hot roasting in a rotary kiln, leaching V and Mo components in a water solution by water leaching of the mixture.
The spent petrochemical desulfurization catalyst contains not only the V and Mo components but also Ni, Fe and Co components, which form spinel phases such as NiOAl2O3, FeOAl2O3 and CoOAl2O3 by the hot roasting. Here, since the spinel phases are not leached by water leaching, residue is formed.
When an oil refining company uses a Ni-containing catalyst, spent catalyst residue containing Ni and Fe is produced. When Co-containing catalyst is used, spent catalyst residue containing Co and Fe is produced.
Since Ni, Fe and Co components in the spent catalyst residue are of a spinel phase, which is chemically stable, they have been buried without being recovered.
According to a method of recovering Ni from the spent chemical desulfurization catalyst, Ni is recovered in the form of NiSO4 by cold roasting (Korean Patent Application No. 1998-0021919).
The Ni-recovering method separates and recovers Ni component in the form of NiSO4 from spent petroleum desulfurization catalyst by oxidizing roasting, ammonium sulfate leaching, solvent extraction and crystallization.
However, this method has to use two roasting steps, expensive leaching agent and solvent extracting agent and is expensive to separate and remove iron. Therefore, the application of this method is restricted.
In addition, there is proposed a method of recovering V and Mo from catalyst using alkali processing of the catalyst, Ni processing in the form of NiO and wet treatment (Korean Patent Application No. 2007-0025283).
This method, however, is not economic since the degree of Ni recovery is very low (57%) and a large amount of expensive alkali agent such as sodium hydroxide has to be used.
Accordingly, up to present, after V and Mo are recovered from the spent petroleum desulfurization catalyst, the entire amount of residue has been buried in most cases.